Corrosion inhibition



United States Patent 3,211,667 CORROSION INl-HBITION Donald M. Coyne, Prairie Village, Kans, and Olen 1L. Riggs, Jr., Ponca City, Okla, assignors to Continental Oil Company, ]Ponca City, Okla, a corporation of Delaware No Drawing. Original application Apr. 13, 1960, Ser. No. 21,891, now Patent No. 3,152,187, dated Oct. 6, 1964. Divided and this application Aug. 17, 1964, Ser. No.

20 Claims. or. 252-392 This application is a divisional application of our c0- pending application Serial No. 21,891, filed April 13, 1960, now Patent Number 3,152,187, isued October 6, 1964.

This invention relates to an improved corrosion inhibiting composition and its method of preparation and use. More particularly it relates to the reaction of an unsaturated diol and a polyalkylene polyamine in the presence of a small concentration of a metallic ion, to form a reaction product possessing superior effectiveness in retarding corrosive attack upon ferrous metals.

Oxygen corrosion is a well-known type of corrosion, and discussion of the problems presented thereby is considered unnecessary. It might be well, however, to discuss filiform corrosion, which is a particularly troublesome and insidious type of corrosive attack.

Filiforrn corrosion was observed and reported as early as 1944 by C. F. Sharman, Filiform Underfilm Cor-' rosion of Lacquered Steel Surfaces, Nature 153, 621 (1944); also Chem. and Ind. (London) 46, 1162. Sharman observed this phenomenon on steel surfaces coated with transparent oil-modified synthetic lacquers in atmospheres containing acetic acid and water vapor, and appreciated the probable importance of the problem in connection with all painted steel surfaces.

Another report on this usual type of corrosion was published by M. Van Loo, D. D. Laiderman, and R. R. Bruhn, in Filiforrn Corrosion, Corrosion 9, 277 (1953). They report the existance of filiform corrosion on ferrous metals, magnesium and aluminum and under tinplate, silverplate, goldplate, and certain phosphate coatings. It was suggested that the type of vehicle or binder represented in the coatings under which filiform had been detected was not critical, and that several vehicles had been examined, such as drying oils and oleoresinous binders, pure and modified phenolic varnishes, alkyds including amine modifications, lacquers, vinyl copolymer coatings and amine modified ether resin and ether ester coatings, in both clear and pigmented films. Van Loo et al. also discuss the fact that a relatively high humidity is an important factor in the growth of filiform corrosion on steel. Following a rather comprehensive theoretical discussion, the authors concluded by indicating that much work yet remained to be done in connection with filiform corrosion and that the known preventative techniques were limited in applicability and effectiveness.

In an article entitled, Mechanism of Filiform Corrosion, Ind. Eng. Chem. 46 (5), 101416, May (1954), V. H. Slabaugh and M. Grotheer present a brief summary of the findings .of Van Loo et al., state the problem, and proceed with a theoretical discussion of the mechanism of filiform.

The above-mentioned prior art thus defines filiform corrosion as a unique type of corrosion characterized by the formation of a maze or network of thread-like corrosion products, each thread usually represented (structurally) by a V-shaped active head and a long inactive body, and further characterized in that its growth is directional (linear and regular rather than radial and haphazard).

It is further recognized: that filiform corrosion occurs on steel at room temperature in the relative humidity 3,211,667 Patented Oct. 12, 1965 range of 65 to that it occurs under organic films which are not impermeable to moisture; and that there is no adequate solution to the problem presented by such corrosion.

We have discovered that filiform corrosion also occurs in an environment containing certain alkanolamines such as diethanolamine. 1020 mild steel strips were immersed in an unstirred, aerated, 1% diethanolamine, 5% sodium chloride brine. A highly directional type of corrosion began at the sharp edges, grew rapidly (up to /2 in. per hour) in the form of thin, threadlike filaments. After 3 days the metal surface beneath the filament was severely corroded. This discovery was significant because there are a number of commonly-occurring situations in which ferrous metals are exposed to alkanolamine systems, for example: soldering and welding fluxes often contain alkanol amines; lacquers used to coat ferrous metals sometimes contain such compounds; and aqueous alkanolamine (diethanolamine) solutions are frequently used for removing acid gases (such as H S=CO mixtures) from gas streams in oil refineries. Filiform corrosion has been a serious problem in the canning industries, where alkanolamines are frequently used in the fluxes employed in the soldering of the seams of the cans.

In the diethanolamine refinery gas sweetening systems corrosion is a serious problem, and we have observed, in the lining of the reactivator reboiler shell of such a system, the threadlike corrosion tracks being characteristic of the phenomenon known as filiform corrosion. Previously-known corrosion inhibitors have not been successful in preventing this serious corrosion. in refinery gas sweetening units, and the use of alloys has been only moderately successful. The use of stainless steel and certain alloys has reduced corrosion rates somewhat; but these materials are expensive.

In the co-pending application of Barnes et al., Serial No. 672,117, filed iuly 16, 1957, now abondoned, the reaction product of the unsaturated diol and the polyalkylene polyamine is disclosed. As indicated in this co-pending application, the butynediols may be prepared by the condensation of acetylene with aldehydes or ketones in the presence of copper acetylide as taught by Reppe et al., in US. Pats. Nos. 2,232,867 and 2,300,969, while the butenediols may be prepared by the partial reduction of the corresponding butynediols by treatment or" the butynediol in an aqueous alkali solution with Zinc in accordance with the Reppe et al. Pat. No 2,267,749. See also the following reports of the British Intelligence Objectives Sub-Committee Surveys (published by His Majestys Stationary Office, London): Re ort No. 30, The Acetylene Industry and Acetylene Chemistry in Germany during the period 1939-1945, 1951, p. 78; Report No. 367, Manufacture of 1:4-Butinediol at I. G. Lugwigshafen.

During the initial work performed prior to the filing of the above-identified application, it was observed that Water was formed during the reaction process, which water was trapped and removed. It was accordingly assumed that the product was not merely an adduct, but was a new compound resuiting from the splitting-0E of water. In order to check these conclusions, purified diols and amines were employed in reactions, and the resulting products were analyzed. In one instance, for example, reactants having the following properties were employed in equimolar quantities:

tion) the filiforrn corrosion of ferrous metals.

The reaction product was distilled in a Claisen flask at 7 mm. taking the fraction from 129-130 C. as the major fraction (69 percent of the total product) having the following properties:

Percent Percent Percent 7113 Carbon H N Observed for produet 51. 5 10. 7 16. 6 1. 4880 Calculated for simple addition product 50.5 11.0 22.1

These data, together with the fact that no Water was trapped in the Dry Ice trap used on the vacuum line during distillation, suggested that the reaction product was a simple addition product rather than a new compound. When distillation was attempted in a spinning band column to obtain a purer product, decomposition occurred, leading to the formation of diol and triamine. The molecular weight of the product could not be determined 40 gms. of solid butynediol was added to a mixture of 80 cc. of ethyl acetate and cc. of toluene plus 0.25 gm. Norit (activated carbon) The mixture was heated on the steam bath to 60 C. and gravity filtered. The filtrate was then cooled, with stirring, by means of a cold water bath. At 35 C. precipitation began. At C. about 70 percent of the material had been removed by precipitation. (Further cooling may cause the slurry to become too thick for handling.) The product was collected on a Biichner funnel and sucked as dry as possible. It was then dried for hours in a vacuum desiccator over sulfuric acid at room temperature.

Another method of purifying 2-butyne-l,4-diol is dis closed in US. Patent 2,789,147, involving technique of slowly cooling the material to crystallize the diol, removing the liquid, and then slowly raising the temperature to sweat out the remaining liquid impurities.

Thus it appeared that when a diol prepared by the Reppe et 211. method Was employed, the reaction thereof with the amine involved the formation of water to yield a condensation product, while the use of a purified diol resulted in the formation of a simple addition product without the splitting-off of water. It was discovered that the condensation product of our invention had corrosion inhibiting properties far superior to the simple addition product. It then became of importance to determine how to prepare the condensation product from a pure diol, in view of the fact that the principal manufacturers of diols were-and still are-preparing and marketing diols of such purity that only the addition product could be prepared therefrom using the technique of the abovernentioned co-pending application.

The principal object of this invention is therefore to provide a new composition matter effective to prevent the corrosion of ferrous metals. Another object is to provide a method for preventing the oxygen corrosion of ferrous metals, involving the addition of a new corrosion inhibiting composition to the corrosive medium surrounding the metal to be protected. Another object is to provide an inhibitor and method of use therefor to prevent Another object of this invention is to provide a novel and effective method of reacting an unsaturated diol and a polyalkylene poly amine involving the use of small amounts of a metal in ionic form to promote or catalyze the reaction. Further objects will become apparent from the consideration of the disclosure which follows.

We have found that the desired condensation products may be prepared from pure diols by incorporating into the reaction mixture of diol and amine a small amount of a metal compound affording a metal ion. Broadly stated, our invention comprises the condensation reaction of an unsaturated diol and a polyalkylene polyamine in the presence of a small amount of a metal compound affording a metal ion, the reaction product formed thereby, and the use of said products to prevent the corrosion of metal surfaces.

Although several metals are suitable, we prefer to use an ionizable copper compound. Although we do not wish to be bound by any theory, it is our opinion that the unpurified diols successfully employed in the reactions of Barnes et a1. (Serial No. 672,117) contained a catalytic amount of copper ion in the form of a copper containing derivative of propargyl alcohol carried over with the propargyl alcohol formed as a by-product during the manufacture of the unsaturated diol. We believe that the copper ion acts as a catalytic agent to promote the condensation reaction between the amine and the diol, possibly involving chelation as a first step followed by condensation, since we have observed that the copper promotes the exothermic formation of an adduct prior to the carrying out of the condensation step of the reaction. The origin of the copper probably lies in the use of copper acetylide as a catalyst for the reaction of the aldehyde and acetylene. It is further believed that when the unsaturated diols were purified to remove the propargyl alcohol therefrom, the copper was removed along with the propargyl alcohol, thus removing the catalyst necessary for the desired reaction of the unsaturated diol with the polyalkylene polyamines. (US. Patent 2,789,147 discloses a method for purifying 2-butyne-1,4-diol to remove propargyl alcohol and other compounds.)

THE UNSATURATED DIOL The unsaturated diols are those of the formula:

where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of CEC- and -CH CH Specific diols include, but are not limited to, the following:

2-butynediol-1,4

l-methyl-Z-butynedioll ,4 1,4-dimethyl-2-butynediol-1,4

1 ,1-dimethyl-2-butynediol-1,4 1,1,4,4-tetramethyl-Z-butynediol-1,4 l-ethyl-2-butynediol-1,4 1,4-diethyl-2-butynediol-1,4

l, 1-diethyl-2-butynediol-1,4 1,1,4,4-tetraethyl-2-butynediol-1,4 l-methyl- 1-ethyl-2-butynediol- 1,4 l-methyl-4-ethyl-2-butynediol-1,4 1,l-dimethyl-4-ethyl-2-butynediol-1,4

1, l -diethyl-4-methyl-2-butynedioll ,4 1,4-diethyl-1-methyl-2-butynediol-1,4 1,1-dimethyl-4,4-diethyl-2-butynediol-1,4 1,1,4-trimethyl-2-butynediol-1,4 1,1,4-triethyI-Z-butynediol-1,4

l ,4-dimethyl-1-ethyl-2-butynediol-l,4 1,1,4-trimethyl-4-ethyl-2-butynediol-1,4 1,4-dimethyl-1,4-diethyl-2-butynediol-1,4 l,1,4-triethyl-4-methyl-2-butynediol-1,4

The butenediols corresponding to the above butynediols, as for example, 2-butenediol-1,4; 1,1-dimethyl-2- butenediol-1,4; 1,1,4,4-tetramethyl-Z-butenedi0l-1-4; and l,4diethyl-l-methyl-2-butenediol-1,4 to name only a few, are also suitable for preparing the reaction products of this invention. The butynediols are preferred, however, because both of the hydroxyl groups are reactive, whereas the butenediols react with more difliculty, so that in actual practice lower yields may be obtained. It is postulated that this is a consequence of the unequal reactivity of the cis and trans forms of the butenediols.

THE POLYALKYLENE POLYAMINE The suitable polyalkylene polyamines may be structurally represented by the formula where R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4.

Exemplary, but not limitative of the polyalkylene polyamines suitable for preparation of the reaction products of our invention, are diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexylamine, dipropylene triamine and tripropylene tetramine.

THE METAL COMPOUND The selection of the metal compound is preferably made from ionizable compounds of chelate-forming metals, which are those metals other than the alkali, alkaline earth, and lanthanide metals. In general, the best chelateformers are cations of small size and high nuclear of ionic charges, such as the metals having atomic numbers of 24-30, 4248, and 7480, although we may employ metals selected from the somewhat broader group of metals including those having atomic numbers of 22-30, 41-48, 49-50, and 73-83, inclusive. As indicated above, we prefer to use a copper compound. Although chloride salts may be employed, we prefer to use other ionizable compounds such as metal acetates or other compounds of organic acids. A particularly suitable compound is copper acetate.

The amount of metallic compound depends somewhat upon the particular reactants and metal used; for example, titanium is more active than copper and, therefore, may be employed in smaller quantities. The amount of metal employed affects the rate of reaction, and since the reaction is exothermic, the desired amount will also depend upon the heat transfer characteristics of the equipment in which the reaction is carried out. It has been established, however, that in the case of copper the amount of metal should preferably not exceed about onehalf gram of metal ion per mole of the unsaturated diol. If this limit is exceeded, the reaction proceeds very rapidly and the resulting product generally contains an excess of a high molecular weight resinous fraction and therefore lacks certain desired physical characteristics such as viscosity and water solubility. We have also found that mere trace quantities of copper in the order of parts of copper acetate, per million parts of diol, are effective to promote the desired reaction involving the splitting-off of water to form the condensation product. We generally use from about 10500, and preferably from about 25-100 parts of copper acetate per million parts of diol. In Examples 1 and 3-6, below, we used considerably more metal than is required. Example 7 illustrates a preferred amount of 50 parts of copper acetate per million parts of diol.

PREPARATION OF THE REACTION PRODUCT The unsaturated diol and the polyalkylene polyamine may be simply mixed (preferably in equimolar quantities, but possibly from about /2.-2 mole equivalents of amine per mole equivalent of the diol) and the metal compound added thereto. We prefer, however, to dissolve the metal compound in a small quantity of water,

and then mix the solution with the diol prior to addition of the amine. The diol is preferably heated slightly to facilitate mixing of the metal compound therewith.

The mixture of diol, amine, and metal compound is then heated slightly to initiate the reaction, in a reaction vessel equipped for the azeotropic removal of water. When the reaction commences, the temperature begins to rise at an accelerated rate, and heating should be discontinued. The water which is formed is trapped and removed and the temperature is allowed to rise slowly until the condensation of water has ceased. After the water of reaction has been removed, the mixture is allowed to cool, an azeotropic solvent such as benzene or toluene is added, and azeotropic distillation conducted to trap out residual water. The solvent is stripped from the mixture after which the then-existing temperature is preferably maintained for about 45 minutes to insure completion of the reaction.

The resulting composition is effective to prevent filiform as Well as oxygen corrosion.

Examples of applications for the reaction products of this invention include inhibition of corrosion in cooling towers and other cooling systems, diethanolamine systems such as refinery gas sweetening units, air drilling and aerated mud systems, brine injection for flooding and/or disposal purposes, ballast systems on sea-going vessels, pipeline cleaning and weighting, incorporation in paint, coating and lacquer formulations where filiforrn corrosion is a problem, and incorporation into diethanol aminebased solder fluxes.

The chemical structure of the product has not been elucidated. Depending upon reaction conditions the product is found to contain mixtures of s bstances of various molecular weights. Gas-liquid phase chromatography studies indicate that more than twelve compounds are formed during the reaction and that individual distillation cuts of the reaction product also contain more than one compound. Infrared analysis showed several groups and various linkages, but positive identification of the reaction product (or any of its constituents) was not deemed feasible. It is believed that this variety of compounds having a wide range of molecular weights is responsible for the corrosion-inhibiting properties of the product.

The following examples illustrate the method of preparation of the corrosion inhibitors of this invention, EX- ample 7 setting forth the preferred procedure.

Example 1 One gram of CuCl -2H O, containing 0.37 gm. of copper ion, was dissolved in about 10 ml. of water, and was then added to 87 gm. of 2-butyne-l,4-diol. The mixture was placed in a standard 3-necked round bottom reaction flask equipped for refluxing and for the removal of water by azeotropic distillation. 189 gm. of tetraethylene pentamine was then poured into the flask, and the temperature raised to about 126 C. At this time the temperature began to rise, and water began to condense. The heating mantle was removed and the flask cooled to prevent a sudden increase in temperature. At 153 C., 31 ml. of water had been trapped. At 200 C., 22 ml. of a light yellow distillate had been trapped, and while the temperature climbed from 200 C. to 225 C., 15 ml. of a dark yellow distillate was trapped. The mixture was cooled to C., and ml. of toluene was added. The heating mantle was replaced, and the mixture was heated to about 0., when reflux of the azeotrope began. Refluxing was continued until the residual water had been trapped-out, as evidenced by the condensation of a small amount of the low boiling reaction mixture which was somewhat yellow in color and which discolored the trapped Water slightly. Then the toluene was stripped, commencing at about 117 C. and ending at about 228 C., after which the mixture was held at the latter temperature for 45 minutes.

to rise to 230 C.

Example 2 The procedure of Example 1 was attempted without the use of either the metal salt or the water. The temperature was raised to 140 C., but there was no pronounced exothermic reaction observed and no distillate obtained. The temperature was raised to 180 C. before a slight amount (about 4 ml.) of a clear distillate was obtained. Upon raising the temperature to 190 C., about 10 ml. of a yellow distillate was obtained. There was still no pronounced exothermic eifect as in Example 1. The mixture was then cooled to about 90 C., and 100 ml. of toluene was added for azeotropic distillation and refluxing. After refluxing until it was apparent that no water was being trapped, the toluene was stripped from about 115 C.- 225 C., and the mixture was held at the latter temperature for about 2 hours. At no time was any water detected.

Example 3 The procedure of Example 1 was followed except that pentaethylene hexylamine was substituted for tetraethylene pentamine. The reaction proceeded in the same man- Example 4 The procedure of Example 1 was repeated except that a cobalt salt was employed instead of CuCl -2H O. 1.4 gm. of CoCl -6H O were dissolved in 10 ml. of Water and the solution was mixed with 87 gm. of 2-butyne-1,4- diol, which was placed in the flask. 189 gm. of tetraethylene pentamine was then poured into the flask. The temperature was raised to 125 C. to initiate the reaction, at which time the temperature began to rise. At 159 C., 31 ml. of water had been trapped, and at 190 C. an additional 14 ml. was obtained. A light yellow distillate came over beginning at about 191 C. After reaching 210 C., the temperature rose rather sharply. The heat was removed, but the temperature rose to 245 C. 33.5 ml. of a dark yellowish distillate was obtained. The mixture was cooled to about 70 C., 100 ml. of toluene added, and the residual water removed by azeotropic distillation. Then the toluene was stripped at from 112 C.228 C. The mixture was held at 228 C. for about 1 hour.

Example The procedure of Example 1 was followed using 1.2 gm. of MnCl '4H O instead of CuCI -ZH O.

Water began to distill130 C. Trapped 21 ml. water163 C. Trapped 25 ml. distillate200 C.

The heat was removed, but the temperature continued 13 ml. of a dark yellow distillate was trapped. After cooling to 75 C., 100 ml. of toluene was added. The azeotrope was refluxed to remove residual water, and the toluene was then stripped (117 C.- 228 C.). The mixture was then held at 225 C. for

about 2 hours.

Example 6 Example 1 was repeated using 1.4 gm. of SnCl -2H O instead of CuCl -2H O.

Water began to distill121 C. Trapped 38 ml. Water166 C. Trapped 12 ml. light yellow distillate-205 C.

The heat was removed but the temperature climbed to 246 C. 10 ml. of a dark yellow distillate was obtained. Residual water was removed by azeotropic distillation while refluxing, and the toluene was then stripped (111 C.-228 C.). The mixture was held at about 225 C. for about 2 hours.

Example 7 Into a 500 ml., 3-necked, round bottom flask, place one mole (86 gm.) of 2-butyne-1,4-diol and 0.86 ml. of a stock solution of copper acetate. (This stock solution consists of 5 gm. of Cu(C H O H O dissolved in 1,000 ml. of de-ionized water heated to 50 C.) The temperature is raised to the melting point of the diol (57-5 8 C.), while stirring, to mix in the copper. To the warm solution add one mole of tetraethylene pentamine (189 grams) while continuing to stir the mixture. Raise the temperature to 180 C. and hold. Water begins to distill over at approximately 170 C. Continue distillation until 1820 ml. of distillate has been trapped. Cool ingredients to 70 C. and add 30 ml. toluene for azeotrope of remaining water. Raise the temperature. Azeotropic distillation begins at approximately 134 C. Trap and remove water only as thimble fills. The temperature will slowly rise with removal of residual water. As the temperature reaches 190 C., measure the water (it should be near 16 ml. volume). Continue to let the temperature rise as toluene is stripped free of the reaction product. The temperature should not be allowed .to exceed about 225 C. A few m1. of a yellow distillate will be trapped out in the toluene at temperatures between 190 C.225 C. The product forms a bright, clear solution in water.

The compositions of Examples 1-7 were tested for inhibition of oxygen corrosion, and the results are shown in Table 1. The indicated quantities of the corrosion inhibitor were dissolved in 250 ml. of an aerated 5 percent sodium chloride solution, and mild steel coupons immersed therein and allowed to stand for the periods of time specified. Thereafter, the coupons were removed, descaled by scrubbing with a nylon bristle brush and a cleaning powder, weighed, and the weight loss determined. The same procedure was followed in the absence of inhibitor to obtain a blank. The percent protection was calculated as follows:

P.C.P.:Percent protection afforded by inhibitor Wb zInitial weight of coupon subjected to test in the absence of inhibitor Wb zFinal weight of coupon subjected to test in the absence of inhibitor Wc zlntial weight of coupon subjected to test in presence of inhibitor Wc zFinal weight of coupon subjected to test in the presence of inhibitor TABLE 1 Concentra- Time of Example Metal I tion of exposure Percent inhibitor (days) protection 286 6 91 143 4 92 143 4 63 143 4 286 6 Manganese. 286 6 92 Tin 286 6 89 7 Copper 286 7 93 The compositions of Examples 1-7 were also tested and found to be efiective in preventing filiform corrosion. Mild steel coupons were immersed in an unstirred, aerated 5 percent sodium chloride solution containing 1 percent dieithanolamine. The corrosion inhibitor was employed in the concentrations indicated in Table 2 which sets 9 forth the results obtained. (Without the use of the inhibitor, a highly directional type of corrosion began at the edges of the coupons, and grew rapidly (u to /2 in. per hour) in the form of thin, thread-like filaments.)

While the foregoing tests were conducted at 143 p.p.m., 286 p.p.m., and 715 p.p.m., corresponding to 100 p.p.m., 200 p.p.m., and 500 p.p.m., respectively of active inhibitor (assuming that the product is 70% active), we have found that concentrations as low as 100 ppm. (total inhibitor) or less are effective to inhibit oxygen corrosion, and that concentrations as low as 200 ppm. (total inhibitor) are effective to prevent filiform corrosion. Optimal concentration is dependent upon the nature of the corrosive fluid and upon the quantity of corrosive constituents present. Where, for example, the system approaches oxygen saturation, the desired degree of inhibitor may be attained through incorporation of from 250-500 or more parts per million. On the other hand, where the system contains very low dissolved oxygen only a few parts per million of the reaction product will give satisfactory results. The quantity to be employed will be readily determinable from the corrosiveness of the solution.

As indicated above, one of the commonly-used methods of removing H 5 and CO from refinery gases involves the treatment of such gases with an alkanolamine. US. Patent Re. 18,958 (original US. Patent 1,783,901, issued December 2, 1930, to Bottoms) described such a process, and is hereby made a part of this specification. Other US. patents relating to the alkanolamine removal of H 8 from hydrocarbon fluids are: 2,157,879, 2,164,194, 2,238,201, 2,220,138, 2,281,356, 2,311,342, and 2,383,416. Refinery sweetening units usually employ diethanolamine solutions, but monoethanolamine is sometimes used. Solutions of monoethanolamine and glycol are employed in the units of many gasoline plants where, in addition to H 5 and CO water is to be removed.

Referring to the drawing of Re. 18,958, the gas sweetening process described therein is as follows. The gases to be purified are introduced to the bottom of the absorber '10, in which they are contacted with the aqueous alkanolamine solution introduced through line 11, and pass from the absorber through line 13. The spent amine solution, after being heated in exchanger 22, is delivered to the top of regenerator 15, in which acid gases are stripped from the amine. The gases from the top of the regenerator are passed to a condenser 24. The cooled acidic gases may thenbe removed by means of line 27, and the condensate trapped and refluxed to the regenerator through line 28. The regenerated amine is taken from the bottom of the regenerator, cooled, and returned to the absorber tower. The re'generator is usually equipped with heating means located near the bottom of the tower. This heating means is shown as a steam coil 18 in Re. 18,958, but is more conveniently a reboiler, separate from the regenerator, but located near the bottom of the tower.

In alkanolamine systems, corrosion is usually found to affect that equipment handling a saturated solution of acid gas as this solution is being vaporized or condensed. In general, the corrosion is most severe in regions where the metal-skin temperature is highest and the acid-gas concentration the greatest. The equipment usually suffering the most severe corrosion includes the reactivator reboiler, the reactivator tower, richto lean-solution heat exchangers, and the acid-gas cooler.

The rate of corrosion taking place in the gas sweetening equipment may be reduced by the addition of a small amount of the above-described reaction product to maintain a concentration of at least 50 parts .per million, and preferably about -200 parts per million, based on the liquid phase. The inhibitor may be added at any convenient point; for example, it may be added to the regenerator overhead line, to the regenerator reflux line, to the reboiler, or at any other covenient point or combination of points. The preferred inhibitor is the reaction product of 2-butyne-1,4-diol and tetraethylene pentamine, although other products are suitable, as indicated above.

Example 8 Several known corrosion inhibitors were added to the filiform-producing diethanolamine (DEA) and monoethanolamine (MEA) systems. These systems consisted of unstirred, aerated, 1% amine, 5% sodium chloride brine solutions. 1020 mild steel strips were immersed in such solutions for periods of 168 hours. The results are presented in Table 3.

TABLE 3.EFFECTS OF CHEMICAL ADDITIVES ON FILIFORM CORROSION IN MEA AND DEA BRINE SYSTEMS Chemical treatment, 100 p.-p.m.: Filiform occurs Tetraethylenepentaminebutynediol reaction product No Diethylenetriamine--butynediol reaction product No Triethylenetetramine-butynediol reaction product No Commercial Imidazoline inhibitor Yes Commercial Rosin Amine D inhibitor Yes Sodium chromate Yes Sodium nitrite Yes Tetraethylenepentamine Yes Diethylenetriamine Yes Triethylene tetrarnine Yes Imidazoline sulfate Yes n-Acetyl ethanolamine Yes Aminoethylethanolamine Yes Dibutylisopropanolamine Yes Phenyl ethanolamine Yes Pyrogallic acid (as an oxygen scavenger) Yes Tetraethylenepentaminepyrogallic acid Yes Example 9 In order to more closely simulate the actual conditions present in a commercial diethanolamine gas treating unit and to thus more vividly illustrate the results afforded by this invention by presenting quantitative data, the following tests Were performed.

A S-necked, l-liter, round-bottom flask was assembled with a steel test coupon suspended therein, and a solution the same as that employed in Example 8 was placed in the flask. The solution was continuously stirred during the test period. A mixture of H 8 and CO gases was passed through the liquid at the rate of 0.5 liter per min. A vertical condenser attached to one neck of the flask prevented evaporation loss. The temperature was main tained at 200 F. during the test period (24- hours). Surface-corrosion observations were made at the end of the test. The weight-loss measurements were determined, from which corrosion rates and percent protection were calculated. The results of this test are shown in Table 4.

TABLE 4.EFFECT OF INHIBITORS ON CORROSION IN A. 1 PERCENT DEA, PERCENT SODIUM CHLORIDE BRINE WITH HYDRO GEN SULFIDE AND CARBON Concen- Corrosion Chemical tration, rate (mils Surface corrosion (parts per per your) million) None 0 96 Fitting. Commercial Imidazoline 250 7. 3 Slight pitting. Commercial Rosin Amine 250 8. 4 Do.

D Tetraethylenepentamine 250 None detected.

butynediol reaction product.

The corrosion which occurred during this test was of the pitting type rather than the threadlike filiform type, because the fluid environment was under agitation which prevents build-up of the threadlike formations. As indicated above, filiform will occur in an unagitated systern.

Example TABLE 5 Corrosion rates Time-exposure of exposed cou- Ohemical treatment interval pons, liquid phase (mils per year) None 11-18-57 to 12158 7. 8 Tetraethylenepentamine- 1-21-58 to l-28-58 5. 9 butynediol. 4. 0

Do 1-28-58 to 2-4-58 While specific details of the method of preparation and use of the inhibitors of this invention have been given for purposes of illustration, it is to be understood that the invention is not limited thereby, but is to be taken as limited solely by the language of the appended claims.

We claim:

1. The method of inhibiting the corrosion of ferrous metals in contact with a corrosive aqueous medium which comprises incorporating into said medium a product formed by the reaction of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of CEC and CH=CH with about %2 mole equivalents of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound affording a chelate-forming metal ion, the amount of said metal compound being suflicient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of water.

2. The method of claim 1 wherein the metal ion is copper, the unsaturated diol is 2-butyne-l,4-diol, and the polyalkylene polyamine is tetraethylene pentamine.

3. The method of claim 1 wherein the metal ion is copper, the unsaturated diol is 2-butyne-l,4-diol, and the polyalkylene polyamnie is pentaethylene hexylamine.

4. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen which comprises incorporating into said medium a product formed by the rection of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of with about /22 mole equivalents of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound affording a chelate-forming metal ion, the amount of said metal compound being sufficient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of Water.

5. The method of claim 4 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is tetraethylene .pentamine.

6. The method of claim 4 wherein the metal ion is copper, the unsaturated diol is 2-butyne-l,4-diol, and the polyalkylene polyamine is pentaethylene hexylamine.

7. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen and sodium chloride which comprises incorporating into said medium a product formed by the reaction of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group Consisting of hydro gen, methyl, and ethyl, and R is selected from the group consisting of with about /z--2 mole equivalent of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound affording a chelateforming metal ion, the amount of said metal compound being sufiicient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of water.

8. The method of claim 7 wherein the metal ion is copper, the unsaturated diol is 2-butyne-.l,4-diol, and the polyalkylene polyamine is tetraethylene pentamine.

9. The method of claim 7 wherein the metal ion is copper, the unsaturated diol is 2-butyne-l,4-diol, and the polyalkylene polyamine is pentaethylene hexylamine.

10. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen, sodium chloride and an amine selected from the 13 group consisting of monoethanolamine and diethanolamine which comprises incorporating into said medium a product formed by the reaction of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of with about /z2 mole equivalent of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound afiording a chelateforming metal ion, the amount of said metal compound being suflicient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of water.

11. The method of claim wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is tetraethylene pentamine.

12. The method of claim 10 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is pentaethylene hexylamine.

13. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen, H S, CO and an amine selected from the group consisting of monoethanolamine and diethanolamine which comprises incorporating into said medium a product formed by the reaction of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of with about /2-2 mole equivalent of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound affording a chelateforming metal ion, the amount of said metal compound being sufficient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of water.

14. The method of claim 13 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is tetraethylene pentamine.

15. The method of claim 13 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is pentaethylene hexylamine.

16. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen, H 8, CO sodium chloride and an amine selected from the group consisting of monoethanolamine and diethanolamine which comprises incorporating into said medium a product formed by the reaction of about one mole equivalent of an unsaturated diol of the formula where R is selected from the group consisting of hydrogen, methyl, and ethyl, and R is selected from the group consisting of with about /2-2 mole equivalent of a polyalkylene polyamine of the formula wherein R is a radical selected from the group consisting of ethylene and propylene, and n is an integer varying from 1 to 4; said reaction being carried out in the presence of a small amount of a compound affording a chelateforming metal ion, the amount of said metal compound being sufficient to cause an exothermic reaction between the unsaturated diol and the polyalkylene polyamine and to cause the formation of water.

17. The method of claim 16 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4diol, and the polyalkylene polyamine is tetraethylene pentamine.

18. The method of claim 16 wherein the metal ion is copper, the unsaturated diol is 2-butyne-1,4-diol, and the polyalkylene polyamine is pentaethylene hexylamine.

19. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen, H S, CO and diethanolamine which comprises incorporating into said medium the product formed by the reaction of approximately equimolar quantities of 2- butyne-1,4-diol and tetraethylene pentamine, said reaction being carried out in the presence of a small amount of copper ion suflicient to cause the liberation of heat and formation of by-product water of reaction.

20. The method of inhibiting the corrosion of ferrous metals in contact with an aqueous medium containing oxygen, H 5, CO and diethanolamine which comprises incorporating into said medium the product formed by the reaction of approximately equimolar quantities of 2- butyne-1,4-diol and pentaethylene hexylamine, said reac tion being carried out in the presence of a small amount of copper ion sufficient to cause the liberation of heat and formation of by-product water of reaction.

References Cited by the Examiner UNITED STATES PATENTS 2,598,213 5/52 Blair et al. 2528.55 3,107,221 10/63 Harrison et a1. 252392 3,107,222 10/63 Riggs 2528.55 3,113,113 12/63 Marsh et a1. 252-392 3,152,187 10/64 Coyne et al 242-392 FOREIGN PATENTS 762,228 11/56 Great Britain.

JULIUS GREENWALD, Primary Examiner. 

1. THE METHOD OF INHIBITING THE CORROSION OF FERROUS METALS IN CONTACT WITH A CORROSIVE AQUEOUS MEDIUM WHICH COMPRISES INCORPORATING INTO SAID MEDIUM A PRODUCT FORMED BY THE REACTON OF ABOUT ONE MOLE EQUIVALENT OF AN UNSATURATED DIOL OF THE FORMULA 